A shock mount currently used in the automotive industry to secure vehicle bodies to vehicle frames is disclosed in U.S. Pat. Nos. 4,783,039 and 4,720,075 to Peterson et al, the disclosures of which are hereby incorporated by reference. This shock mount has been successful in the industry due to its design features which provide a telescoping metal spacer and metal thimble assembly that snap together to hold the thimble and spacer together until secured with a threaded fastener, and in which the thimble and spacer have mating surfaces to prevent either one from rotating relative to the other, thereby permitting fastening of the threaded fastener with minimal undesirable rotation of one element relative to the other.
While this known shock mount is exceptionally effective and has high strength characteristics, it does not allow for variations in strength requirements. For example, in some instances an automotive or truck manufacturer may specify that the shock mount will not separate in a barrier test, i.e., that the shock mount will not separate when the vehicle in which it is used impacts a barrier at a certain speed. In other instances, the vehicle manufacturer may specify that the shock mount will separate during a barrier test at certain speeds. Such a specification can arise when the vehicle manufacturer is designing crash protection features in which the energy of a crash is dissipated by destruction or separation of various components of the vehicle body. In such case, each shock mount must be separately designed and manufactured, increasing product cost.
These problems were addressed by the shock mount disclosed in U.S. Pat. No. 5,570,067 to Peterson et al, the disclosure of which is hereby incorporated by reference. This shock mount includes interfitting flanged spacer and thimble members and resilient rings mounted thereto. The thimble is formed from a hollow plastic stem and a metal base. The metal base includes a flange and an internally threaded post. The thimble stem fits over and snaps onto the post. The metal base member is made in either a high strength or low strength configuration. Selection of the appropriate configuration of base member provides a shock mount assembly of the desired separation strength.
While this shock mount design provides some flexibility as to the separation strength, in that either the high strength or the low strength configuration can be used, accommodating multiple separation strengths would require that base members having multiple configurations be manufactured. Such a process would require design work to determine appropriate configurations for the desired separation strength and retooling of the manufacturing machinery to produce such configurations, thereby increasing cost of production. Moreover, even after the appropriate design configuration is determined, variations in material gauge and chemistry may greatly affect the separation strength. Thus, two shock mounts having the same configuration may separate at widely varying impact forces.
What is desired therefore is a shock mount which has the capability to be used in both the fixed and breakaway applications described above, which allows for selectivity of the force required for separation, which is economic to produce, and which reliably separates at the desired impact force.